This invention relates to technology for processing mail sent from a secure mailing list using public key infrastructure or the like, and particularly to technology for, when it has not been possible to decrypt an encrypted mail, requesting that the encrypted mail be re-sent by an encryption method such that it can be decrypted.
Encrypted mail sent using a secure mailing list sometimes cannot be decrypted (cannot be read) by a user, because of the user's environment. In this case, it is desirable for the user who has been unable to decrypt the encrypted mail to send to the secure mailing list server a re-send request requesting that the encrypted mail be re-sent. And furthermore it is desirable that the re-sent mail be decryptable by the user without fail.